1. Field of the Invention
This invention relates to polymeric reducing agents for oxidized developing agents and to silver halide photographic elements containing such reducing agents for oxidized developing agents.
It is known in the art to add reducing agents (hereinafter called scavengers or D.sub.ox scavengers) for oxidized developing agent (hereinafter called D.sub.ox) to photographic elements in order for the scavenger to interact with the oxidized developing agent and prevent it from reacting at an undesired location or at an undesired point in time. These scavengers have two primary applications. One use is in interlayers (i.e. a non-imaging layer between two imaging layers), where the scavenger decreases or eliminates wrong-color image formation caused by D.sub.ox migration between layers of different colors. The second use of such scavengers is in image-forming layers where the compounds function to reduce stain in areas of low dye formation (i.e. in the D.sub.min). In this use, the scavenger can also control the characteristic curve shape of the film and improve granularity in multilayer systems. When coated in emulsion layers, the scavengers are referred to as competitors, because they compete with the image-forming compounds in the reaction with oxidized developing agent. In general, the requirements for an effective competitor are more demanding than for an effective interlayer scavenger.
A satisfactory scavenger has the following characteristics:
1) has high activity toward oxidized developer. PA1 2) does not form colored products (stain) after reaction with oxidized developer. PA1 3) has no unwanted interactions with other film components such as image-forming compounds or dyes. PA1 4) can be easily coated in photographic layers. PA1 5) does not crystallize in the coating solution during the coating process or in the film. Crystallization can lead to coating defects and reduced or variable activity. PA1 6) remains immobile in the layer in which it is coated during the coating process, during the ageing of the film, and during the image development process. PA1 7) is stable during the natural ageing of the film. PA1 8) development of silver halide emulsions. PA1 9) can be easily manufactured.
Of this list, requirements 1, 3, and 8 are more critical for the use of a scavenger as a competitor than as an interlayer scavenger. One reason for this is that the competitor is coated directly with silver halide and other film components such as dye-forming compounds. Also, in order to reduce D.sub.min stain, the competitor must have higher reactivity toward D.sub.ox than the dye-image forming compound. In comparison, an interlayer scavenger of lower activity may function effectively as an interlayer scavenger as long as it can reduce D.sub.ox before it diffuses through the entire interlayer.
The use of substituted hydroquinone scavengers is well-known. Specific examples of the uses and various types of hydroquinones are disclosed in U.S. Pat. Nos. 2,243,294, 2,360,290, 2,403,721, 2,728,659, 2,732,300, 3,700,453, 4,198,239, 4,732,845, and West German OLS 2,149,789.
Polymeric scavengers which incorporate hydroquinone structures have been described in U.S. Pat. Nos. 4,345,016 and 4,983,506. Ballasted sulfonamidophenol and disulfonamidophenol scavengers have been described in U.S. Pat. Nos. 4,366,226 and 4,205,987, and in Research Disclosure 15162, November 1976. U.S. Pat. Nos. 4,474,874, 3,457,079, 4,476,219, and European Patent Application 115,305 disclose scavengers which are ballasted gallic esters and amides.
These scavenger compounds described above are generally hydrophobic and crystalline. They are introduced into photographic materials by the various known dispersion methods. These include oil-in-water dispersions, which are prepared by dissolving the compound in a high-boiling organic solvent together with a low-boiling solvent, and emulsifying the resulting solution with an aqueous gelatin solution containing a surfactant. The low-boiling organic solvent may then be removed by evaporating with heat under low pressure or by washing the dispersion with chilled water if the solvent is water-miscible. Other dispersion methods include dispersion in a latex, alkali dispersions, and solid microcrystalline dispersions. The dispersion process is labor-intensive and can introduce photographic variability, the added organic solvent increasing the total thickness of the film layers as well as possibly causing environmental problems because of the presence of solvents. Many ballasted compounds have a tendency to crystallize in the dispersion, severely affecting photographic performance, while the less hydrophobic compounds tend to diffuse between layers in the photographic packages.
Most of the scavengers described above are deficient in one or more of the requirements previously described for a satisfactory scavenger. Many ballasted hydroquinones have low or moderate activity toward oxidized developer and are unstable toward aerial oxidation during the natural ageing of photographic elements. This instability also leads to the formation of by-products which can fog silver halide emulsions. Disulfonamidophenol compounds are known to form a substantial yellow stain upon reaction with oxidized developing agents. Many of the compounds, including many gallic esters and amides, tend to crystallize after dispersion in a photographic element.